I. Field of the Invention
The present invention is directed to a system for water drainage, and more particularly to a subsurface system for draining water from beneath covered ground, such as the subbase of a roadway.
II. Description of the Prior Art
A major cause of damage to road surfaces is the entrapment or retention of water beneath the road surface, in the road base or subbase. Such retained water can cause potholes, buckles and gaps in the pavement, as well as cracking or crumbling of the pavement, and can lead to premature collapse or failure of the roadbed. Rapid subsurface drainage of the roadbed is thus critical to extending the useful life of the highway.
The (HYDRAWAY) (trademark of Monsanto Chemical Company, St. Louis, Mo.) drain is a known drainage system useful for this purpose. It comprises a tubular, internally supported geotextile fabric filter disposed in the ground beneath or preferably adjacent a covered ground surface, for example, in the subbase of a highway or pavement. The filter support is constructed of a somewhat rigid but resiliently deformable polyethylene core, about which the filter is circumferentially disposed, and to which the filter is bonded. This known drain is asserted to have flow characteristics two to three times better than those of conventional sand-backfilled drainage systems. The Hydraway drain is also asserted to be more resistant to clogging from dirt, gravel and sand transported by the water drained through the system.
The filter and contained support of the Hydraway drain are generally rectangular, conveniently 12, 18 or 36 inches wide, about 1 to 3 inches thick, and variable in length, preferably up to 200 to 400 feet long. A filter dimensioned in this fashion is particularly advantageous in its ease of installation; a 4 inch wide trench of appropriate depth is dug by a conventional trencher, and an appropriately dimensioned boot can position the drain against the inside wall of the trench, in a continuous process of installation. The trench can conveniently be immediately backfilled with the just-excavated material, which reduces the amount of "spoils" which need to be removed. The trench is sufficiently narrow that settling of the adjacent ground is minimized, and is sufficiently narrow to avoid entrapment of vehicle tires therein, if traffic encroaches upon the highway shoulder. The cost and delay of backfilling with sand or an aggregate is thus also avoided. Additionally, the cost of manufacture of the Hydraway drain is asserted to be significantly less than the costs of conventional drains.
One drawback of the Hydraway drainage system lies in the outlet and union structures employed in it. These structures fluidly connect an open end of the tubular filter to a drainpipe or to other filters. Several inconveniences have arisen during the use of these structures. The exit end of the filter slips into an open end of the outlet member or other structure employed, and is retained in place by an encirling piece of fabric carried by the outlet or other structure, or by stapling and wrapping with tape. This is disadvantageous in the amount of time and effort needed to be certain that the filter has not caught the fabric piece in the open outlet end, and needed to manipulate the fabric piece to extend it sufficiently over the filter to attach the filter to the outlet or structure. Of course, such attachment is hardly secure, as the filter may slide from the outlet or other structure if pulled during installation, or stressed during settling of the ground after installation. Moreover, the open end of the outlet or other structure is dimensioned very closely to the outside diameter of the filter. If the area of installation is muddy or gravelly, sliding of the filter into the opening may be hindered, and mud or gravel may be trapped between the fabric of the filter and the retaining fabric on the outlet. Additionally, the outlet is dimensioned only to accomodate a standard 4 inch drainpipe. The outlet requires a separate adapter fitting if it is desired to instead affix the outlet to a conventional flexible pipe. The known adapter fitting includes a piece of standard diameter pipe which must be bonded to the outlet. These drawbacks are costly in that they create trouble or delay precisely at the point of installation, after the trench has been cut, and after the "spoils" are exposed to the elements. Such disadvantages with known systems are likely to be even more noticable in instances where an outlet serves to join two or more sections of filter inlet tubes and also serves as a drain connection.